MADISON – If the future scenarios being churned out by the world’s most sophisticated computer climate models are on the mark, big changes are in store for Wisconsin’s weather during the next century.
Using a realistic estimate of future global carbon emissions, University of Wisconsin-Madison scientists are forecasting significantly warmer winters, altered patterns of precipitation and more severe weather events for the Badger state.
Those changes, according to the Wisconsin researchers, will be layered on a climate that, based on temperature and precipitation measurements from around the state over the past 60 years, has already warmed 1.3 degrees Fahrenheit, on average, and 2.5 degrees Fahrenheit in the winter.
“Looking into the future, we are anticipating that by 2050 Wisconsin will have an annual mean warming of between 4 and 9 degrees Fahrenheit,” says Dan Vimont, a UW-Madison professor of atmospheric and oceanic sciences, who, along with colleagues Chris Kucharik, David Lorenz and Michael Notaro, developed estimates of the state’s future climate as well as a chart of climate change in Wisconsin’s recent past.
The future climate projections were developed through the UW-Madison Nelson Institute for Environmental Studies in support of the Wisconsin Initiative for Climate Change Impacts (WICCI), a partnership with the Wisconsin Department of Natural Resources and others to assess the potential impacts of climate change on Wisconsin industry, natural resources and human health. The new study was primarily funded by Wisconsin Focus on Energy.
“Wisconsin is not necessarily getting hotter, but it is getting less cold,” says Kucharik, a UW-Madison professor of agronomy and environmental studies. “The biggest changes we’ve seen over the last 60 years have been on the low end of the temperature scale, not the high end.”
For example, since 1950, the number of days each winter when the temperature fell below zero degrees Fahrenheit has diminished by five days in southern Wisconsin and by 12 to 18 days in northwest Wisconsin. The decline represents a 10 to 30 percent reduction in the frequency of very cold days.
However, for the future the models also show a doubling of the number of very hot summer days, those where temperatures exceed 90 degrees F, in the southern part of the state from an average of 12 to 25 by mid-century, and a near tripling from and average of five to 12 very hot days in the north.
Northern Wisconsin’s springs and winters will also likely be wetter than in the past, with precipitation expected to increase in that part of the state on average by 10 percent in the spring and 20 percent in the winter.
“The models don’t agree about precipitation changes in the summer, but there is a robust increase in winter precipitation,” says Vimont. “Combined with the enhanced winter warming, that also means we’ll see a big increase in rain events in mid-winter.”
The biggest climate shifts, both historic and projected, are in the spring and winter, according to the UW-Madison researchers.
“In the long run, especially for the southern part of the state, we’re going to see a shorter winter,” Vimont says, adding that it is possible that the state may see more freezing rain and less snow, especially in the south.
Moreover, very intense weather events, such as the 14-inch downpour that breached the shoreline of Lake Delton in 2008, are forecast to become even more intense and possibly more frequent, according to Kucharik and Vimont.
The Wisconsin researchers arrived at their projections using more than a dozen of the sophisticated models scientists use to forecast global climate change. They were programmed to assess future climate based on the A1B carbon emissions scenario developed by the Intergovernmental Panel on Climate Change (IPCC), which portrays a future world of rapid economic growth, stable population, and rapid introduction of new and more efficient technology. The results, however, were tuned to a much finer resolution, a grid scale of eight kilometers, and can account for landforms and water as potential climate influences. The result is one of the most detailed and comprehensive regional climate projections for any state.
Vimont emphasizes that the projections for Wisconsin’s future climate are pegged to a range of potential outcomes as the data are intended to help working groups within WICCI develop strategies for adapting to a different climate. “We’ve done this in a way to reflect the range of possibilities for the future,” Vimont explains. “We’ve stayed very true to that. We’ve provided a very flexible database.”
The forecast of Wisconsin’s future climate was requested on behalf of WICCI to provide its various working groups with possibilities for the future. The groups – which range from fisheries and forestry to human health and stormwater – need to have a feel for how climate might change in the future, say Kucharik and Vimont.
This story, with an FAQ and slide show of climate model maps, is available at http://www.news.wisc.edu/Wisconsin-climate-2009.html